Objective To estimate two-week prevalence rate of diarrhea and explore the influencing factors of diarrhea among the children under the age of 3 years in rural Lhasa. Method A Cross-sectional design with multi-stage cluster random sampling method was adopted in this study,and a face-to-face interview was conducted to collect the information of socio-economic household and diarrhea within two weeks.All information was obtained by recalling from the respondents. Results The two-week prevalence rate of diarrhea among the children was 17.3%.The prevalence was higher in boys (17.6%) than girls (16.9%),but the difference was not significant (P＞0.05).The two-week prevalence rates of diarrhea among children with different age groups were 16.5%,28.4%,25.0%,10.9%,9.8%,and 4.9% in 0~5,6~11,12~17,18~23,24~29,and 30~35 months aged group,respectively.The differences of prevalence among the different age groups were significant (P＜0.05),and the prevalence was highest in 6~11 months of age.The Logistic regression model was used to analysis the possible influencing factors of two-week diarrhea among the children under the age of 3 years.Finally,the factors such as the age of children,whether catch a cold in the past two weeks,the poorer sight of mother at night during pregnancy than before,the age of children when added protein complimentary foods and the pan used to cook in family had strong relationships with the two-week prevalence rate of diarrhea among children (P<0.05). Conclusion The two-week prevalence rate of diarrhea among the children under the age of 3 years is high in rural Lhasa.In order to reduce the two-week prevalence rate of diarrhea,the mother should be educated on how to raise their children,strengthening nutrient supplementation during pregnancy,and introducing protein complementary foods timely should be especially promoted by the local government.